1. Field of the Invention
In general, the present invention relates to systems and methods that are used to steam reform hydrocarbons to generate a volume of hydrogen rich gases and then separate the hydrogen from such gases for separate use. More particularly, the present invention relates to the structure of reaction chambers where gas shift reactions are produced and where hydrogen permeable membranes are used to separate hydrogen gas.
2. Prior Art Description
In industry, there are many applications for the use of ultra pure hydrogen. For instance, there are many PEM fuel cells that operate using hydrogen. The hydrogen, however, must be ultra pure. In the art, ultra pure hydrogen is commonly considered to be hydrogen having purity levels of at least 99.999%. Any molecules of carbon dioxide, carbon monoxide or other contaminant gases that are received by the fuel cell either reduces its efficiency or causes damage to the fuel cell.
Free hydrogen gas does not exist naturally on earth to any significant extent. This is because hydrogen reacts with many elements and readily combines to form more complex molecules. As a consequence, hydrogen gas must be manufactured by removing it from other more complex molecules. Hydrogen gas can be manufactured in a number of ways. For instance, hydrogen gas can be created by splitting water molecules through electrolysis. However, the power needed for electrolysis is always significantly greater than the power available from a fuel cell that utilizes the output hydrogen gas from the electrolysis. Any fuel cell system that obtains hydrogen gas from electrolysis, therefore, results in a net power loss.
Techniques have been developed where hydrogen gas can be extracted from a hydrocarbon fuel and water mixture that has undergone an endothermic reaction. This initial endothermic reaction occurs between 350° C. and 1000° C. depending mostly on the initial hydrocarbon fuel being used. In the steam reforming process, the hydrocarbon fuel and water are converted in an endothermic reaction principally into hydrogen (H2), carbon monoxide (CO), methane (CH4), carbon dioxide (CO2) and water (H2O). The amount of energy required depends on the type of fuel being reformed. In steam reforming, a principal challenge is efficiently supplying the endothermic energy as the cracking of the fuel and steam proceeds.
The useful chemical energy in the resultant gases is contained in the H2, CO, CO2 and CH4. The chemical energy in these three resultant gases contains the chemical energy that was originally in the hydrocarbon fuel, plus some of the endothermic energy that was used to heat the reaction.
The resultant gases of H2, CH4, CO and CO2 are mixed with steam at an elevated temperature typically of between 300° C. and 450° C. In this temperature range, a water gas shift reaction is induced. Once the water gas shift reaction is induced, the CO present in the resultant gases reacts with the water (H2O). The CO and the H2O react as follows:CO+H2O→CO2+H2 It can therefore be seen that additional hydrogen gas is created by the water gas shift reaction. The hydrogen gas is then purified by drawing the hydrogen gas through a hydrogen permeable membrane in a hydrogen separator. The purified hydrogen can then be used to power a fuel cell or serve some other industrial purpose.
In the prior art, obtaining purified hydrogen from a hydrocarbon is typically a two-step process. In the first step, the hydrocarbon is reacted with water in a reaction chamber to create reaction gases. In a second step, the reaction gases are introduced into a hydrogen separator in order to separate out the purified hydrogen. In production, the two most important and expensive components in generating hydrogen are the reactor and the separator. Although these components are separate in the prior art, it has been learned that significant cost savings and efficiencies can be obtained by integrating the reaction chamber and the hydrogen separator into a single integrated component.
In U.S. Pat. No. 8,889,098, the Applicant herein set forth a design for a hydrogen processor that integrates a reaction chamber and a separator into a single unit that utilizes concentric tubes. In the Applicant's earlier patent, the hydrogen processor is heated by orienting the concentric tubes vertically and providing a flame under the bottom end of the concentric tubes. In theory, the heat from the flame should travel up along the exterior of the tube formation to heat the full length of the tube formation. However, in practice this heating scheme has flaws. Inevitably, the end of the tube formation closest to the flame becomes hotter than the rest of the tube. The remainder of the tube becomes cooler the further it travels from the source of the flame. As a result, in order to have a hydrogen processor with an average optimal operating temperature, that hydrogen processor will embody sections that are both cooler and hotter than the average optimal temperature. This uneven temperature detracts from the efficiency of the hydrogen processor.
A need therefore exists for a design of an integrated hydrogen processor with an improved heating scheme that can efficiently maintain a selected operating temperature during operation. This need is met by the present invention as described and claimed below.